In this research article by Jennifer Y F Wu and colleagues (BMJ 2006;333:522-5, 9 Sep, doi: 10.1136/bmj.38905.447118.2F) we failed to spot an error in the abstract. In the final sentence of the results section, the second set of confidence intervals should be 1.80 to 4.57 (not 1.80 to 2.57).